The quote attributed to Stallman is made up and is a distortion of his actual views.
He created GNU as an operating system. His position is that when talking about the GNU OS, it is appropriate to call it GNU/linux if it’s running the linux kernel, though he is also fine with calling it GNU.
Not to mention it’s a made up rule that doesn’t apply to literally any other acronym (radar, sonar, NASA, NATO, scuba, etc.)